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Mathematical Charts and Tables

Conversion Tables

Conversion Tables

As has been suggested already, instructive mathematical charts introduced unfamiliar units of measure. A number of handy tables also were produced to assist in conversions. Perhaps the earliest such chart in the collections dates from about 1814, and is designed to convert from units divisible by twelfths to decimal units. The size of conversion factor and the way the numbers are written suggest that it was made to convert from Massachusetts pounds and shillings to U.S. currency. By the mid-20th century, the dollar prevailed throughout the United States, and Americans were more concerned with understanding foreign currencies when they traveled abroad. Toward that end, some purchased a slide chart called the UNICON, which allowed them to convert between dollars and numerous foreign currencies when they knew the exchange rate.

Engineers have long needed to perform conversions as part of their work. In the first half of the 20th century, manufacturers sometimes distributed small advertising cards that listed decimal equivalents of parts of an inch. Larger tables might list a large number of useful conversion factors. New efforts to introduce metric weights and measures in the United States in the 1970s led to the distribution of a range of cards and slide charts that eased conversions. These were distributed by organizations ranging from the federal government to a manufacturer of outdoor clothing and camping supplies to a producer of food emulsifiers and flavorings.

This rule consists of a clear plastic envelope, glued together along the back bottom edge, and a white plastic slide. The front of the rule has six windows for reading off conversions between yards or feet and meters; centimeters and inches; square yards and square meters; square centimeters and square inches; cubic meters and cubic yards; and liters and imperial gallons or U.S. gallons. The front also has tables of equivalents and a scale for converting between Fahrenheit and Celsius temperatures. The top right corner is marked: GRINDSTED (/) PRODUCTS, INC. (/) Research for quality (/) 2701 ROCKCREEK PKY. (/) NORTH KANSAS CITY, (/) MISSOURI 64116. It is also marked: TEL: 816-842-6500 (/)TELEX: 4-2565 (/)GRINDSINC NKSC. A table for decimal equivalents between fractions, millimeters, and inches runs down the middle of the slide.

The back has six windows for reading off conversions between pounds and kilograms; ounces and grams; PSI and atmospheres or kilograms per square centimeters; inches or centimeters of mercury and PSI; BTU and kilocalories or watt hours; and meter-kilograms and foot-pounds or joules. The back also has more tables of equivalents.

Grindsted is a Danish brand for bulk food products, such as animal feed and emulsifiers for human foods. In 1989 it merged into the Danish conglomerate Danisco, which in turn was purchased by DuPont in 2011. The logo on this rule was in use from 1975 to 1991. Grindsted's factory in the Kansas City suburbs opened in 1975 and filed an annual report in 2012. Compare this rule to metric converters 1990.0689.01 and 1990.3231.01. For the style of manufacture, compare to 1988.0795.02.